When Justin Palmer stumbled across a dataset that included the year nearly every building in the Portland metro area was built, he was curious how old the buildings on his block are. Instead of just searching the data for his neighbors’ addresses, he made the beautiful map above.

He posted the map on his website, and it soon caught the eye of other mapmakers. Just a few days later, Thomas Rhiel published a similar map of Brooklyn, spurred by New York City’s release of a huge dataset known as PLUTO. Pretty soon, more maps began popping up. Soon there was a map of all of New York City, one of Reykjavik, Iceland, and one of Ljubljana, Slovenia, each with its own amazing colors, patterns and stories.

These maps make more than just pretty pictures. Palmer learned from his map that Portland’s oldest building identifiable by name was built in 1851. Only 942 structures are left from the 1890s while 75,434 built in the 1990s are still standing. Palmer graphed the steep and steady decline of new buildings since 2005.

Inspired by Palmer’s map, Marko Plahuta made a map of building ages in his home town of Ljubljana, Slovenia. When he plotted the number of buildings built each year, the graph had some huge spikes in it, and he set about discovering why. One spike occurred four years after a major earthquake hit the area in 1899 when people were able to rebuild. Similar periods of rebuilding show up after the two world wars. Plahuta made a really nice video of his map that shows the growth of the city from 1500-2013.

The Netherlands has a wonderful dataset that includes the almost 10 million buildings in the entire country, which inspired two beautiful maps in this gallery.

From the moment I saw the map of Portland, I wanted to make a map like that for the San Francisco Bay Area. The only problem was, I had no idea how to make the map, or really any sort of map. But with Rhiel’s help, I’ve made a start on my own map of building ages and I’ll show you how you can make one too.

The maps of building ages collected here are the best I’ve seen out there so far. On each slide, there’s a link to the interactive version of the map, information about each author, and even notes on the making of some of the maps. If you know of some more, let us know. (Thanks to Google Maps Mania for pointing me to some of these.)